Predicting protein function and orientation on a gold nanoparticle surface using a residue-based affinity scale.

The orientation adopted by proteins on nanoparticle surfaces determines the nanoparticle's bioactivity and its interactions with living systems. Here, we present a residue-based affinity scale for predicting protein orientation on citrate-gold nanoparticles (AuNPs). Competitive binding between protein variants accounts for thermodynamic and kinetic aspects of adsorption in this scale.

Understanding the Adsorption of Peptides and Proteins onto PEGylated Gold Nanoparticles.

Polyethylene glycol (PEG) surface conjugations are widely employed to render passivating properties to nanoparticles in biological applications. The benefits of surface passivation by PEG are reduced protein adsorption, diminished non-specific interactions, and improvement in pharmacokinetics. However, the limitations of PEG passivation remain an active area of research, and recent examples from the literature demonstrate how PEG passivation can fail.

Solution NMR of Nanoparticles in Serum: Protein Competition Influences Binding Thermodynamics and Kinetics.

The spontaneous formation of a protein corona on a nanoparticle surface influences the physiological success or failure of the synthetic nanoparticle as a drug carrier or imaging agent used . A quantitative understanding of protein-nanoparticle interactions is therefore critical for the development of nanoparticle-based therapeutics. In this perspective, we briefly discuss the challenges and limitations of current approaches used for studying protein-nanoparticle binding in a realistic biological medium.

Quantitative Measurement of Multiprotein Nanoparticle Interactions Using NMR Spectroscopy.

An effective intensity-based reference is a cornerstone for quantitative nuclear magnetic resonance (NMR) studies, as the molecular concentration is encoded in its signal. In theory, NMR is well suited for the measurement of competitive protein adsorption onto nanoparticle (NP) surfaces, but current referencing systems are not optimized for multidimensional experiments. Presented herein is a simple and novel referencing system using N tryptophan (Trp) as an external reference for H-N 2D NMR experiments.

Quantification of the Photon Absorption, Scattering, and On-Resonance Emission Properties of CdSe/CdS Core/Shell Quantum Dots: Effect of Shell Geometry and Volumes.

Reliable quantification of the optical properties of fluorescent quantum dots (QDs) is critical for their photochemical, -physical, and -biological applications. Presented herein is the experimental quantification of photon scattering, absorption, and on-resonance-fluorescence (ORF) activities of CdSe/CdS core/shell fluorescent QDs as a function of the shell sizes and geometries. Four spherical QDs (SQDs) with different diameters and four rod-like QDs (RQDs) with different aspect ratios (ARs) have been analyzed using UV-vis, fluorescence, and the recent polarized resonance synchronous spectroscopic (PRS2) methods.

Linear Extrapolation of the Analyte-Specific Light Scattering and Fluorescence Depolarization in Turbid Samples.

Anisotropy and depolarization are two interconvertible parameters in fluorescence and light scattering spectroscopy that describe the polarization distribution of emitted and scattered photons generated with linearly polarized excitation light. Whereas anisotropy is more frequently used in fluorescence literature for studying association/dissociation of fluorophore-bearing reagents, depolarization is more popular in the light-scattering literature for investigating the effect of scatterers' geometries and chemical compositions. Presented herein is a combined computational and experimental study of the scattering and fluorescence depolarization enhancement induced by light scattering in turbid samples.

A Divide-and-Conquer Strategy for Quantification of Light Absorption, Scattering, and Emission Properties of Fluorescent Nanomaterials in Solutions.

Optical properties of fluorescent materials including their UV-vis absorption, scattering, and on-resonance fluorescence activities are strongly wavelength-dependent. Reported herein is a divide-and-conquer strategy for experimental quantification of fundamental optical constants of fluorescent nanomaterials including their UV-vis absorption, scattering, and on-resonance-fluorescence (ORF) cross-section spectra and ORF fluorescence and light scattering depolarization spectra. The fluorophore UV-vis extinction spectrum is first divided into a blue and a red wavelength region.

Surface Plasmon Resonance, Formation Mechanism, and Surface Enhanced Raman Spectroscopy of Ag-Stained Gold Nanoparticles.

A series of recent works have demonstrated the spontaneous Ag adsorption onto gold surfaces. However, a mechanistic understanding of the Ag interactions with gold has been controversial. Reported herein is a systematic study of the Ag binding to AuNPs using several and measurement techniques.

Optical Properties and Kinetics: New Insights to the Porphyrin Assembly and Disassembly by Polarized Resonance Synchronous Spectroscopy.

With their unique photochemical properties, porphyrins have remained for decades the most interested chemicals as photonic materials for applications ranging from chemistry, biology, medicine, to photovoltaic. Porphyrins can self-assemble into higher order structures. However, information has been scant on the kinetics and structural evolution during porphyrin assembly and disassembly.

Scattering and absorption differ drastically in their inner filter effects on fluorescence, resonance synchronous, and polarized resonance synchronous spectroscopic measurements.

The sample inner filter effect (IFE) induces spectral distortion and affects the linearity between intensity and analyte concentration in fluorescence, Raman, surface enhanced Raman, and Rayleigh light scattering measurements. Existing spectrofluorometric-based measurements treat light scattering and absorption identically in their sample IFEs. Reported herein is the finding that photon scattering and absorption differ drastically in inducing the sample IFE in Stokes-shifted fluorescence (SSF) spectrum, resonance synchronous spectrum (RS2), and the polarized resonance synchronous spectrum (PRS2) measurements.

Synthesis of C-Unsubstituted 1,2-Diazetidines and Their Ring-Opening Reactions via Selective N-N Bond Cleavage.

C-Unsubstituted 1,2-diazetidines, a rarely studied type of four-membered heterocyclic compounds, were synthesized through an operationally simple intermolecular vicinal disubstitution reaction. 1,2-Diazetidine derivatives bearing various N-arylsulfonyl groups were readily accessed and studied by experimental and computed Raman spectra. The ring-opening reaction of the diazetidine was explored and resulted in the identification of a selective N-N bond cleavage with thiols as nucleophiles, which stereoselectively produced a new class of N-sulfenylimine derivatives with C-aminomethyl groups.

Quantification of Material Fluorescence and Light Scattering Cross Sections Using Ratiometric Bandwidth-Varied Polarized Resonance Synchronous Spectroscopy.

Presented herein is the ratiometric bandwidth-varied polarized resonance synchronous spectroscopy (BVPRS2) method for quantification of material optical activity spectra. These include the sample light absorption and scattering cross-section spectrum, the scattering depolarization spectrum, and the fluorescence emission cross-section and depolarization spectrum in the wavelength region where the sample both absorbs and emits. This ratiometric BVPRS2 spectroscopic method is a self-contained technique capable of quantitatively decoupling material fluorescence and light scattering signal contribution to its ratiometric BVPRS2 spectra through the linear curve-fitting of the ratiometric BVPRS2 signal as a function of the wavelength bandwidth used in the PRS2 measurements.

Quantification of Gold Nanoparticle Ultraviolet-Visible Extinction, Absorption, and Scattering Cross-Section Spectra and Scattering Depolarization Spectra: The Effects of Nanoparticle Geometry, Solvent Composition, Ligand Functionalization, and Nanoparticle Aggregation.

Using the recent polarized resonance synchronous spectroscopic (PRS2) technique, we reported the quantification of photon extinction, absorption, scattering cross-section spectra, and scattering depolarization spectra for AuNPs of different sizes and shapes. The effects of the solvent composition, ligand functionalization, and nanoparticle aggregation on the AuNP photon absorption and scattering have also been experimentally quantified. The light scattering depolarization is close to 0 for gold nanospheres (AuNSs) crossing the entire UV-vis region but is strongly wavelength-dependent for gold nanorods (AuNRs).